DHCP Server enable/disable change needs filter_configure

I was checking what filter rules come and go when DHCP Server is enable or disabled on an interface. I discovered that the pf ruleset was not being rebuilt. I had to go and do some other edit/save to rules or aliases to trigger the filter_configure.
When DHCP Server is enabled or disabled on an interface, the filter rules should be rebuilt so they include or not mention DHCP as per the new DHCP Server setting.
Note: this is also a fix for 2.1 - it should apply cleanly there. When you commit this, can you do the magic to also apply it to the 2.1 branch?